Heat-conductive dielectric polymer material and heat dissipation substrate containing the same

ABSTRACT

A heat-conductive dielectric polymer material includes a thermosetting epoxy resin, a nonwoven fiber component, a curing agent and a heat-conductive filler. The thermosetting epoxy resin is selected from the group consisting of end-epoxy-function group epoxy resin, side chain epoxy function group epoxy resin, multi-functional epoxy resin or the mixture thereof. The thermosetting epoxy resin comprises 4%-60% by volume of the heat-conductive dielectric polymer material. The curing agent is configured to cure the thermosetting epoxy resin at a curing temperature. The heat-conductive filler comprises 40%-70% by volume of the heat-conductive dielectric polymer material. The nonwoven fiber component comprises 1%-35% by volume of the heat-conductive dielectric polymer material. The heat-conductive dielectric polymer material has a thermal conductivity greater than 0.5 W/mK.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates to a heat-conductive dielectric polymermaterial and a heat dissipation substrate containing the same, and moreparticularly to a heat-conductive dielectric polymer material havingfiber component and a heat dissipation substrate containing the same.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 37 CFR 1.98.

In recent years, the white light emitting diode (LED) has gainedconsiderable attention worldwide as an important new technology withbroad applications and numerous benefits. LED technology offers theadvantages of having a small volume, low power consumption, longlifetime, a favorable reaction speed, and overcomes many of the problemsof incandescent lamps. LED technology is used in many applications,including backlights for the LCD displays, mini-projectors, illuminatorsand light sources for vehicles, attracting increasing attention.

However, in high-power LEDs used for illumination, only about 15%-20% ofthe power inputted into the LED is converted into light, while theremaining 80%-85% is converted into heat, and the heat cannot bedissipated to the environment at the appropriate time. Thus, theinterfacial temperature of the LED component is excessively high,thereby affecting the intensity of the emitted lights and the lifetime.Therefore, heat management of LED components becomes increasinglyimportant.

FIG. 1 is a schematic view of a heat dissipation substrate 10conventionally applied in an electronic component (e.g., an LEDcomponent, not shown). The heat dissipation substrate 10 includes aheat-conductive dielectric material layer 12 and two metal foils 11respectively stacked on the upper and lower surfaces of theheat-conductive dielectric material layer 12. The electronic componentis disposed above the upper metal foil 11. The conventional process forforming the heat dissipation substrate 10 includes the following steps.First, a liquid epoxy resin and a heat-conductive filler (e.g., aluminumoxide particles) are mixed, and then a curing agent is added, so as toform a slurry. Gas contained in the slurry is then removed through avacuum process and the slurry is coated on the lower metal foil 11. Theupper metal foil 11 is then disposed on the surface of the slurry toform a composite structure of metal foil/slurry/metal foil. Next, thecomposite structure is hot-pressed and cured to form the heatdissipation substrate 10, in which the slurry is formed into theheat-conductive dielectric material layer 12 upon being hot-pressed andcured.

However, the conventional art is limited by the property of the slurryand has the following disadvantages: (1) the conventional art must befinished within a specific time; otherwise, the slurry will cure andcannot be coated on the metal foil, causing a waste of the slurry; and(2) when the hot-press step is conducted in the conventional art, aquantity of slurry flows out of the two metal foils 11, and a separationbetween solid and liquid occurs upon reaching the hot-press temperature,thus, the heat-conductive filler is non-uniformly distributed in theheat-conductive dielectric material layer 12, thereby affecting the heatdissipation efficiency of the heat dissipation substrate 10.Furthermore, the slurry is difficult to be stored and the flexibility ofthe process for forming the heat dissipation substrate is limited by theviscosity of the slurry (e.g., heat dissipation substrates withdifferent shapes cannot be fabricated efficiently).

In other words, the slurry of the mixture of the liquid epoxy resin, theheat-conductive filler and the curing agent is coated on a metalsubstrate, and is heated to B-stage and hot-pressed to form a circuitboard. Likewise, as to a FR4 circuit board, epoxy resin is coated on aglass fiber cloth and then is heated to B-stage, and then it undergoeshot-press to form a glass fiber circuit board.

The above process uses slurry with low viscosity in which solid-liquidseparation occurs due to the precipitation of heat-conductive filler.Consequently, the slurry is not evenly mixed and the efficiency of heatdissipation is decreased. Moreover, the slurry is not easily stored.Because the thermal conductivity of the glass fiber cloth is low, forexample, approximately 0.36 W/mK, the circuit board using the glassfiber cloth performs poor heat dissipation efficiency.

In summary, known heat-conductive circuit board uses slurry with lowviscosity, and thus solid-liquid separation will occur easily. Moreover,the circuit board having glass fiber cloth performs poor heatdissipation behavior due to the low thermal conductivity of glass fibercloth. Therefore, it is desirable to develop a heat-conductivedielectric material serving as high efficient heat dissipation mediumfor circuit boards.

BRIEF SUMMARY OF THE INVENTION

An aspect of the present application is to provide a heat-conductivedielectric polymer material, which contains nonwoven fiber component andthus is rubbery, thereby enhancing its processibility and heatdissipation property.

In another aspect, the present application provides a heat dissipationsubstrate containing the heat-conductive dielectric polymer material,which has a preferable heat dissipation property and a high voltageresistant dielectric property.

The present application discloses a heat-conductive dielectric polymermaterial having a fiber component. The heat-conductive dielectricpolymer material includes a polymer component, a nonwoven fibercomponent, a curing agent and a heat-conductive filler. The polymercomponent includes a thermosetting epoxy resin. The curing agent isconfigured to cure the thermosetting epoxy resin at a curingtemperature. The nonwoven fiber component and the heat-conductive fillerare uniformly dispersed in the polymer component. In an embodiment, theheat-conductive filler comprises 40%-70% by volume of theheat-conductive dielectric polymer material, whereas the nonwoven fibercomponent comprises 1%-35% by volume of the heat-conductive dielectricpolymer material. The heat-conductivity of the heat-conductivedielectric polymer material is larger than 0.5 W/mK.

In an embodiment, the thermosetting epoxy resin of the polymer componentmay be end-epoxy-function group epoxy resin, side chain epoxy functiongroup epoxy resin, multi-functional epoxy resin or the mixture thereof.The thermosetting epoxy resin comprises 4%-60% by volume of theheat-conductive dielectric polymer material.

In an embodiment, the nonwoven fiber component may include inorganicceramic fiber, organic polymer fiber or the mixture thereof. Forexample, glass fiber, aluminum oxide fiber, carbon fiber, polypropylenefiber, polyester fiber, or the mixture thereof. In terms of shapes, thenonwoven fiber component may include a chopped strand fiber.

In an embodiment, the polymer component may further includethermoplastic. In other words, thermoplastic is added to thethermosetting epoxy resin, and they are mutually soluble and form ahomogeneous mixture before curing. Thus, the heat-conductive filler canbe uniformly dispersed in the mixture to obtain optimal heat-conductiveefficiency. Due to the properties of the thermoplastic and the fibercomponent, the heat-conductive dielectric polymer material can be moldedby a thermoplastic process such as extrusion, calendaring or injectionmolding. Furthermore, the thermosetting epoxy resin can be cured andcross-linked at a high temperature, so that the thermoplastic and thethermosetting epoxy resin form an inter-penetrating network (IPN)structure, which not only has the thermosetting plastic properties ofgood high temperature deformation resistance and the thermoplasticproperties of tenacious and non-brittle characteristics, but also can bestrongly adhered to metal electrodes or a substrate.

The present application further discloses a heat dissipation substrate,which comprises a first metal layer, a second metal layer and a layercontaining the aforementioned heat-conductive dielectric polymermaterial. The heat-conductive dielectric polymer material layer issandwiched between and in physical contact with the first metal layerand the second metal layer. The metal layers and the thermosettingplastic are combined by hydrogen bonding or Van der Waals force, and themetal layers subjected to chemical surface treatment can be used to formmore stable chemical bonding with the thermosetting plastic. Theheat-conductive dielectric polymer material layer can withstand avoltage larger than 2000 volts in the case that the heat-conductivedielectric polymer material layer has a thickness of 0.1 mm.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present application will be described according to the appendeddrawings in which:

FIG. 1 shows a known heat dissipation substrate for electronic deviceapplications; and

FIG. 2 shows a heat dissipation substrate in accordance with anembodiment of the present application.

DETAILED DESCRIPTION OF THE INVENTION

The heat-conductive dielectric polymer material of the presentapplication includes a polymer component, a nonwoven fiber component, acuring agent and a heat-conductive filler. The polymer componentincludes a thermosetting epoxy resin, which comprises 4% to 60%,preferably 6% to 50%, and especially preferably 8% to 40% by volume ofthe heat-conductive dielectric polymer material. The curing agent isused to cure the thermosetting epoxy resin at a curing temperature. Theheat-conductive filler is uniformly dispersed in the polymer component,and comprises 35% to 75%, preferably 40% to 70%, and most preferably 45%to 65%, by volume of the heat-conductive dielectric polymer material.The nonwoven fiber component comprises 1%-35%, preferably 2%-30% andmost preferably 3%-25% by volume of the heat-conductive dielectricpolymer material. The thermal conductivity of the heat-conductivedielectric polymer material is greater than 0.5 W/mK, preferably greaterthan 1.0 W/mK, and most preferably greater than 1.5 W/mK.

FIG. 2 is a schematic view of a heat dissipation substrate 20 of thepresent application. The heat dissipation substrate 20 includes a firstmetal layer 21, a second metal layer 22, and a heat-conductivedielectric polymer material layer 23 having a nonwoven fiber component24. The heat-conductive dielectric polymer material layer 23 is inphysical contact with the first metal layer 21 and the second metallayer 22, and in an embodiment at least one of the interfaces is a microrough surface 25 that includes a plurality of nodular protrusions 26with the diameters mainly distributed between 0.1 μm and 100 μm, so asto enhance the tensile strength therebetween. The nodular protrusions 26may include copper, nickel, zinc or arsenic plated layer, or organicsilicon, organic titanium coatings.

The methods for fabricating the heat-conductive dielectric polymermaterial layer 23 and the heat dissipation substrate 20 are described asfollows. First, the thermosetting epoxy resin and the fiber componentare mixed while being heated at 170° C. for 30 minutes, so as to form auniform mixture. The heat-conductive filler is then added into theuniform mixture, and they are mixed evenly to form a uniform rubberymaterial. The curing agent and an accelerating agent are then added intothe uniform rubbery material having the fiber component at a temperatureof 80° C. A hot-press process is then used to dispose the uniformrubbery material between two release films at 100° C., which is thenleveled under a pressure of 30 kg/cm², so as to form the heat-conductivedielectric polymer material layer 23, which is a lamella-shapedheat-conductive dielectric composite material. In order to fabricate theheat dissipation substrate 20, the two release films are stripped offfrom the upper and lower surfaces of the heat-conductive dielectricpolymer material layer 23. Next, the heat-conductive dielectric polymermaterial layer 23 is melt extruded at the temperature at least 30° C.below the curing temperature of the curing agent, and is sandwichedbetween the first metal layer 21 and the second metal layer 22, andafter being hot-pressed for 30 minutes at 160° C. to crosslink theheat-conductive dielectric polymer layer to form a crosslinked heatdissipation substrate 20 with a thickness of, for example, 0.2 mm. Thelamella-shaped heat-conductive dielectric composite material has thenonwoven fiber component, thereby enhancing the rigidity thereof andpreventing the substrate from bending that may be caused by hot-press.Because the polymer component has a relatively high viscosity (about 10⁵to 10⁷ poise), solid-liquid separation will not occur. The material ofthe first metal layer 21 and the second metal layer 22 may be selectedfrom copper, nickel, or another metal processed by means ofelectroplating or other physical coating methods. The appearance of thelamella-shaped heat-conductive dielectric composite material is rubbery(not slurry); thus, it is easily stored and processed. Moreover, theheat-conductive dielectric composite material can be processed by amethod commonly used for processing thermoplastic, thereby enhancing itsprocessibility.

Table 1 shows the composition of the heat-conductive dielectric polymermaterial layer used in the heat dissipation substrate in accordance withthe four embodiments (Em 1 to Em 4) of the present application and acomparative example (Comp). Table 2 shows appearance, thermalconductivity of the heat-conductive dielectric polymer material layer,and the corresponding voltage resistance according to Em 1 to Em 4 andComp. The thickness of the heat-conductive dielectric polymer materiallayer in each embodiment and comparative example is approximately 0.2mm.

TABLE 1 Component (volume %) Heat- Liquid epoxy conductive resin Curingagent Glass Polyester filler Al₂O₃ DER331 100S/UR500 fiber fiber (PET)Em 1 40 28 1.6/0.4 30 0 Em 2 55 28 1.6/0.4 15 0 Em 3 55 28 1.6/0.4 7 8Em 4 70 25.1 1.5/0.4 3 0 Comp 60 37.3 2.2/0.5 0 0

TABLE 2 Melt Break- extrusion Thermal down Uncured Separation tolamella- conductivity Voltage appearance (100° C.) shaped film (W/mK)(KV) Em 1 Rubbery No Yes 0.51 9.6 Em 2 Rubbery No Yes 1.46 8.5 Em 3Rubbery No Yes 1.48 8.6 Em 4 Rubbery No Yes 2.83 6.9 Comp Slurry Yes No1.98 7.9

Table 3 shows the composition of the heat-conductive dielectric polymermaterial layer used in the heat dissipation substrate in accordance withfive embodiments (Em 5 to Em 9) of the present application, in whichthermoplastic is further added to increase impact resistance andstrength of the material. Table 4 shows appearance, thermal conductivityof the heat-conductive dielectric polymer material layer, and thecorresponding voltage resistance according to Em 5 to Em 9. Thethickness of the heat-conductive dielectric polymer material layer ineach embodiment is approximately 0.2 mm.

TABLE 3 Component (volume %) Heat- Liquid Curing conductive epoxyThermo- agent Polyester filler resin plastic 100S/ Glass fiber Al₂O₃DER331 Phenoxy UR500 fiber (PET) Em 5 40 23.4 10 1.3/0.3 25 0 Em 6 4016.9 30 0.9/0.2 12 0 Em 7 55 21.5 7 1.2/0.3 8 7 Em 8 55 12.2 17 0.6/0.28 7 Em 9 70 21.5 5 1.2/0.3 2 0

TABLE 4 Melt extrusion to lamella- Thermal Breakdown Uncured Separationshaped conductivity Voltage appearance (100° C.) film (W/mK) (KV) Em 5Rubbery No Yes 0.51 9.2 Em 6 Rubbery No Yes 0.52 9.0 Em 7 Rubbery No Yes1.49 8.5 Em 8 Rubbery No Yes 1.47 8.8 Em 9 Rubbery No Yes 2.91 7.2

The particle sizes of the heat-conductive filler Al₂O₃ in Tables 1 and 3are between 5 and 45 μm, which is produced by Denki Kagaku KogyoKabushiki Kaiya Company. The liquid epoxy resin adopts the DER331™ ofDow Chemical Company, which is a thermosetting epoxy resin. The curingagent adopts a dicyandiamide (Dyhard 100S™) of Degussa Fine ChemicalsCompany, and accelerating agent is UR-500. The thermoplastic is anultra-high molecular phenoxy resin PKHH™ from the Phenoxy Associateswith a weight average Mw of larger than 30000.

It can be known from Tables 1 and 2 that, in Em 1-4 of the presentapplication, after the curing agent is added, the thermosetting epoxyresin (liquid epoxy resin is used in the Em 1-4 and Comp in Table 1) isreacted with the nonwoven fiber component such as glass fiber andpolyester fiber to form a fiber-reinforced structure, thus, the obtainedheat-conductive dielectric polymer material layer has a rubberyappearance and is suitable for melt extrusion, and solid-liquidseparation will not occur during the hot-press at 100° C. Moreover,according to the thermal conductivity and breakdown voltage shown inTable 2, the four embodiments of the present application can indeed meetthe requirements for the heat dissipation conditions of electroniccomponents. However, the comparative example (Comp) without adding fibercomponent shows slurry appearance before curing, and solid-liquidseparation occurs during hot-press process. In addition, theheat-conductive dielectric polymer material of the comparative examplecannot be melt-extruded to a lamella-shaped film, and thus it is noteasily processed.

It can be known from Tables 3 and 4 that, in Em 5-9 of the presentapplication, in addition to the thermosetting epoxy resin and thenonwoven fiber component, the thermoplastic is further introduced. Afterthe curing agent is added, the thermosetting epoxy resin is reacted withthe thermoplastic to form an IPN structure. Thus, the obtainedheat-conductive dielectric polymer material layer exhibits reinforcedrubbery behavior and is suitable for melt extrusion process, andsolid-liquid separation will not occur during hot-press process.According to the thermal conductivity and breakdown voltage shown inTable 4, the embodiments of the present application can indeed satisfythe requirements for the heat dissipation conditions of electroniccomponents.

According to Tables 1-4, the thermal conductivities are greater than 0.5W/mK, preferably greater than 1.0 W/mK, most preferably greater than 1.5W/mK, and voltage endurance characteristics are greater than 500V/0.1mm, preferably 2000V/0.1 mm, and most preferably 3000V/0.1 mm.

According to the aforementioned embodiments, the heat-conductivedielectric polymer material uses nonwoven fiber component tosignificantly enhance rigidity and support behavior thereof. Moreover,the IPN structure may be further introduced, in which the thermoplasticand the thermosetting epoxy resin in the heat-conductive dielectricpolymer material are substantially mutually soluble. The term“substantially mutually soluble” means that the thermoplastic and thethermosetting epoxy resin are mixed to form a solution having a singleglass transition temperature. The thermoplastic and the thermosettingepoxy resin are mutually soluble; thus, when mixed together, thethermoplastic is dissolved into the thermosetting epoxy resin, so thatthe glass transition temperature of the thermoplastic is substantiallyreduced, and the mixing process is allowed to be conducted under atemperature lower than the normal softening temperature of thethermoplastic. The formed mixture (i.e., the polymer component) isrubbery (or solid) at room temperature and thus is easily weighted andstored. For example, even if the thermosetting epoxy resin is a liquidepoxy resin, the mixture formed by mixing with the thermoplastic can befabricated into a tough leathery film. At 25° C., the mixture has arelatively high viscosity (about 10⁵ to 10⁷ poise), which is sufficientto prevent filler from settling or redistribution in the polymer matrix.However, the mixture has a sufficiently low viscosity (about 10⁴ to 10⁵poise at 60° C.) at common mixing temperatures (about 40° C. to 100° C.)to allow the added curing agent and heat-conductive filler to beuniformly distributed in the mixture and be reacted. Many examples ofthe mixture can be obtained with reference to U.S. patent applicationSer. No. 07/609,682 (filed on 6 Nov. 1990 and abandoned now) and PCTPatent Publication No. WO92/08073 (published on 14 May 1992), which areboth incorporated herein by reference.

The curing temperature T_(cure) of the curing agent in theheat-conductive dielectric polymer material of the present applicationis higher than 80° C. or preferably higher than 100° C., which is usedto cure (i.e., crosslink or catalytic-polymerize) the thermosettingepoxy resin. The curing agent is used to quickly cure the thermosettingepoxy resin under a temperature higher than the mixing temperatureT_(mix), in which the mixing temperature T_(mix) refers to thetemperature at which the thermoplastic, the thermosetting epoxy resin,and the curing agent are mixed together, and the mixing temperatureT_(mix) is usually about 25° C. to 100° C. When the curing agent ismixed at the mixing temperature T_(mix), a substantial curing will notbe induced. The amount of the curing agent in the present applicationcauses the thermosetting epoxy resin to be cured at a temperature higherthan the mixing temperature T_(mix). Preferably, the curing agent willnot induce a substantial curing at a temperature of lower than about 80°C. or 100° C., and accordingly, the heat-conductive dielectric polymermaterial remains substantially uncured at 25° C. for at least half ayear.

The aforementioned thermosetting epoxy resin may be an uncured liquidepoxy resin, a polymerized epoxy resin, a phenolic epoxy resin or abisphenol A epoxy resin. The thermosetting epoxy resin may be a mixtureof a plurality of epoxy resins, and may include end-epoxy-function groupepoxy resin, side chain epoxy function group epoxy resin,multi-functional epoxy resin or the mixture thereof. Also, thethermosetting epoxy resin may comprise mono-functional group,bi-functional group, tri-functional group, multi-functional group or themixture thereof. In an embodiment, side chain epoxy function group epoxyresin may use NAN YA Plastic corporation NPCN series, e.g., NPCN-703, orChang Chun Group BNE-200.

Besides the materials listed in Tables 1 and 3, the thermosetting epoxyresin in the heat-conductive dielectric polymer material of the presentapplication also can be selected from the thermosetting resin defined in“Saechtling International Plastic Handbook for the Technology, Engineerand User, 2nd (1987), pp. 1-2, Hanser Publishers, Munich.” In anembodiment, the thermosetting epoxy resin usually comprises 4% to 60%,preferably 6% to 50%, and especially preferably 8% to 40% by volume ofthe heat-conductive dielectric polymer material. The thermosetting epoxyresin preferably has a functionality of larger than 2. At roomtemperature, the thermosetting epoxy resin is liquid or solid. If curedwithout adding thermoplastic, the thermosetting epoxy resin is rigid orrubbery. The thermosetting epoxy resin is preferably uncured epoxyresin, and especially uncured epoxy resin defined by ASTM D 1763. Theliquid epoxy resin can be further understood with reference to thedescription in “Volume 2 of Engineered Materials Handbook, EngineeringPlastics, Publisher: ASM International, Pages 240-241.” The term “epoxyresin” refers to a conventional dimeric epoxy resin having at least twoepoxy functional groups, an oligomeric resin, or a polymeric resin. Theepoxy resin is a reaction product of bisphenol A with epichlorohydrin, areaction product (novolac resin) of phenol with formaldehyde, a reactionproduct of epichlorohydrin, cycloaliphatics, peracid epoxy resin withglyceryl ether, a reaction product of epichlorohydrin with p-aminophenol, a reaction product of epichlorohydrin with glyoxal tetraphenol,phenolic epoxy resin or bisphenol A epoxy resin. Commercially availableepoxide ester is preferably 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexane formate (e.g., ERL 4221 of Union Carbide Company orCY-179 of Ciba Geigy Company) or bis(3,4-epoxycyclohexylmethyl) adipate(e.g., ERL 4299 of the Union Carbide Company). Commercially availablediglycidyl ether of bisphenol A (DGEBA) may be selected from Araldite6010 of Ciba Geigy Company, DER 331 of Dow Chemical Company, and Epon825, 828, 826, 830, 834, 836, 1001, 1004, or 1007 of Shell ChemicalCompany. Moreover, the polyepoxidized phenol formaldehyde novolacprepolymer may be selected form DEN 431 or 438 of Dow Chemical Companyand CY-281 of Ciba Geigy Company. The polyepoxidized cersol formaldehydenovolac prepolymer may be selected from ENC 1285, 1280, or 1299 of CibaGeigy Company. The poly polyol glycidyl ether is selected from AralditeRD-2 (based on butyl-1,4-diol) of the Ciba Geigy Company or Epon 812(based on glycerol) of Shell Chemical Company. A suitable diepoxide ofalkylcycloalkyl hydrocarbon is vinyl cyclohexane dioxide, e.g., ERL 4206of Union Carbide Company. Moreover, a suitable diepoxide of cycloalkylether is bis(2,3-diepoxycyclopentyl)-ether, e.g., ERL 0400 of UnionCarbide Company. Moreover, the commercially available flexible epoxyresin includes polyglycol diepoxy (e.g., DER 732 and 736 of the DowChemical Company), diglycidyl ether of linoleic dimer acid (e.g., Epon871 and 872 of Shell Chemical Company), and diglycidyl ether ofbisphenol, wherein the aromatic ring is connected by a long aliphaticchain (e.g., Lekutherm X-80 of the Mobay Chemical Company).

Moreover, the thermosetting epoxy resin having multi-functional groupmay be selected from DEN 4875 (solid novolac epoxy resin) of DowChemical Company, Epon 1031 (tetra-functional solid epoxy resin) ofShell Chemical Company and Araldite MY 720(N,N,N′,N′-tetraglycidyl-4,4′-methylene dianiline) of Ciba-GeigyCompany. Moreover, the difunctional epoxy resin (dicyclic oxide) may beselected from HPT 1071 (solid resin,N,N,N′,N′-tetraglycidyl-a,a′-bis(4-aminophenyl)P-Di-Isopropylbenzene),HPT 1079 of Shell Chemical Company (solid diglycidyl ether ofbisphenol-9-fluorene) or Araldite 0500/0510 (triglycidyl ether ofpara-aminophenol) of Ciba-Geigy Company.

The curing agent used in the present application may be selected fromisophthaloyl dihydrazide, benzophenone tetracarboxylic dianhydride,diethyltoluene diamine, 3,5-dimethylthio-2,4-toluene diamine,dicyandiamide (obtained from Curazol 2PHZ of the American CyanamidCompany) or DDS (diaminodiphenyl sulfone, obtained from Calcure ofCiba-Geigy Company). Moreover, the curing agent may be selected fromsubstituted dicyandiamide (e.g., 2,6-xylylbiguanide), solid polyamide(e.g., HT-939 of Ciba-Geigy Company or Ancamine 2014AS of Pacific AnchorCompany), solid aromatic amine (e.g., HPT 1061 and 1062 of ShellChemical Company), solid anhydride hardener (e.g., pyromelliticdianhydride (PMDA)), phenolic resin hardener (e.g., poly(p-hydroxystyrene), imidazole, the adduct of 2-phenyl-2,4-dihydroxymethylimizoleand 2,4-diamino-6[2′-methylimizole(1)]ethyl-s-triazinylisocyanate),boron trifluoride, and amine complex (e.g., Anchor 1222 and 1907 ofPacific Anchor Company), and trimethylol propane triacrylate.

For the thermosetting epoxy resin, the curing agent is preferablydicyandiamide and is used together with an accelerating agent. Thecommonly used accelerating agent for curing includes urea or ureacompounds; for example, 3-phenyl-1,1-dimethylurea,3-(4-chlorophenyl)-1,1-dimethylurea,3-(3,4-dichlorophenyl)-1,1-dimethylurea,3-(3-chloro-4-methylphenyl)-1,1-dimethylurea and imidazole (e.g.,2-heptadecylimidazole, 1-cyanoethyl-2-phenylimidazole-trimellitate, or2-[.beta.-{2′-methylimidazol-(1′)}]-ethyl-4,6-diamino-s-triazine).

If the thermosetting epoxy resin is urethane, then the curing agent canuse blocked isocyanate, (e.g., alkyl phenol blocked isocyanate selectedfrom Desmocap 11A of Mobay Corporation) or phenol blocked polyisocyanateadduct (e.g., Mondur S of Mobay Corporation). If the thermosetting epoxyresin is unsaturated polyester resin, then the curing agent can useperoxide or other free radical catalysts, such as dicumyl peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl cumyl peroxide, and2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne. Moreover, the unsaturatedpolyester resin may be crosslinked through irradiation (e.g., anultraviolet radiation, a high-power electron beam, or γ radiation).

Some thermosetting epoxy resin can be cured without using a curingagent. For example, if the thermosetting epoxy resin is a bismaleimide(BMI), the BMI are cross-linked under a high temperature, and aco-curing agent (e.g., O,O′-diallyl bisphenol A) may be added togetherto make the cured BMI tougher.

The above epoxy resin cross-linked by using a peroxide crosslink agent,high-power electron beam, or γ radiation is preferably added with anunsaturated cross-linking aid, e.g., triallyl isocyanurate (TAIC),triallyl cyanurate (TAC) or trimethylol propane triacrylate (TMPTA).

The nonwoven fiber component may be ceramic fiber or organic polymerfiber. For example, glass fiber, aluminum oxide fiber, carbon fiber,polypropylene fiber, polyester fiber or the mixture thereof. Thenonwoven fiber component comprises 1%-35%, preferably 2%-30% and mostpreferably 3-25% by volume of the heat-conductive dielectric polymermaterial.

In an embodiment, the thermoplastic comprises 1%-40%, or preferably2%-30%, by volume of the heat-conductive dielectric polymer material.The thermoplastic may include a hydroxy-phenoxyether polymer structure.The hydroxy-phenoxyether may be formed by a polymerization reaction ofthe stoichiometric mixture including diepoxide and difunctional species.The diepoxide is an epoxy resin with an epoxy equivalent weight of about100 to 10000, such as diglycidyl ether of bisphenol A, diglycidyl etherof 4,4′-sulfonylbisphenol, diglycidyl ether of 4,4′-oxybisphenol,diglycidyl ether of 4,4′-dihydroxybenzophenone, diglycidyl ether ofhydroquinone, and diglycidyl ether of 9,9-(4-hydroxyphenyl)fluorine. Thedifunctional species is dihydric phenol, dicarboxylic acid, primaryamine, dithiol, disulfonamide, or bis-secondary amine. The dihydricphenol may be selected from the group consisting essentially of4,4′-isopropylidene bisphenol (bisphenol A), 4,4′-sulfonylbisphenol,4,4′-oxybisphenol, 4,4′-dihydroxybenzophenone, and9,9-bis(-hydroxyphenyl)carbazole. The dicarboxylic acid may be selectedfrom the group consisting essentially of isophthalic acid,terephthalamic acid, 4,4′-biphenylenedicarboxylic acid, and2,6-naphthalenedicarboxylic acid. The bis-secondary amine may beselected from the group consisting essentially of piperazine, dimethylpiperazine, and 1,2-bis(N-aminomethyl)ethane. The primary amine may beselected from the group consisting essentially of 4-methoxyaniline and2-aminoethanol. The dithiol may be 4,4′-dimercaptodiphenyl ether. Thedisulfonamide may be selected from the group consisting essentially ofN,N′-dimethyl-1,3-benzenedisulfonamide, andN,N′-bis(2-hydroxyethyl)-4,4-biphenyldisulfonamide. Moreover, thedifunctional species may be a mixture comprising two differentfunctional groups for being reacted with the epoxide group, for example,salicylic acid and 4-hydroxybenzoic acid.

Moreover, the thermoplastic in the heat-conductive dielectric polymermaterial of the present application may be selected from the groupessentially consisting of a reaction product of liquid epoxy resin withbisphenol A, bisphenol F, or bisphenol S, a reaction product of liquidepoxy resin with a diacid, and a reaction product of liquid epoxy resinwith amines.

In an embodiment, the thermoplastic in the heat-conductive dielectricpolymer material of the present application may be selected from thesubstantially amorphous thermoplastic resin, and its definition can beobtained with reference to Page 1 of “Saechtling International PlasticHandbook for the Technology Engineer and User, Second Edition, 1987,Hanser Publishers, Munich.” The term “substantially amorphous” meansthat the proportion of the part of “crystallinity” in the resin is atmost 15%, and preferably 10%, and especially preferably 5%, for example,a crystallinity of 0% to 5%. The substantially amorphous thermoplasticresin is a high-molecular polymer, which is rigid or rubbery at roomtemperature, and the thermoplastic resin is used for providing theproperties of strength and high viscosity when the above polymercomponent is substantially uncured. The substantially amorphousthermoplastic may be selected from the group consisting essentially ofpolysulfone, polyethersulfone, polystyrene, polyphenylene oxide,polyphenylene sulfide, polyamide, phenoxy resin, polyimide,polyetherimide, polyetherimide/silicone block copolymer, polyurethane,polyester, polycarbonate, and acrylic resin (e.g., polymethylmethacrylate, styrene/acrylonitrile, and styrene block copolymers).

In an embodiment, the aforementioned thermoplastic may include anultra-high molecular phenoxy resin that may have a molecular weight ofgreater than 10000. The thermoplastic may include hydroxy phenoxy etherpolymer. In an embodiment, diepoxide is polymerized with difunctionalspecies to yield the hydroxy phenoxy ether polymer. The thermoplasticcan be generated by reacting the liquid epoxy resin with the bisphenolA, the liquid epoxy resin with a divalent acid, or the liquid epoxyresin with amines.

The heat-conductive filler may include one or more kinds of ceramicpowders, and may be nitride, oxide, or a mixture thereof. The nitridemay be selected from the group consisting essentially of zirconiumnitride, boron nitride, aluminum nitride, and silicon nitride. The oxidemay be selected from the group consisting essentially of aluminum oxide,magnesium oxide, zinc oxide, silicon oxide or titanium oxide. As usual,the oxide has low thermal conductivity, whereas the nitride cannot befilled with a large amount. Therefore, the mixture of oxide and nitridecan overcome the shortcomings.

The heat-conductive dielectric polymer material may be made by thefollowing method. The fiber component, the thermosetting epoxy resin andthe thermoplastic (optionally) are blended and heated at around 200° C.for 30 minutes to form a uniform glue. The heat-conductive filler isadded to the uniform glue to form a uniform rubbery material, and then acuring agent (Dicy) and an accelerating agent are added to the uniformrubbery material at a temperature higher than 80° C. to form the curedheat-conductive dielectric polymer material having an IPN structure.Because the thermoplastic and the thermosetting epoxy resin are mutuallysoluble and homogeneous, the heat-conductive filler is uniformlydistributed in the IPN structure to achieve optimal heat conductiveefficiency.

The nonwoven fiber component can provide stable structure so that theheat-conductive dielectric material is tenacious and non-brittle. Theheat-conductive dielectric polymer material including the thermoplasticcan be processed by thermoplastic methods because it performs like athermoplastic polymer. Moreover, the heat-conductive dielectric polymermaterial also includes a thermosetting plastic so that the thermoplasticand thermosetting epoxy resin can be cross-linked at a high temperatureto form an IPN structure. This structure has the characteristics of athermosetting plastic of good high temperature deformation resistance,and has tenacious, non-brittle characteristics similar to those of athermoplastic, and can easily and firmly adhere to metal electrodes or asubstrate.

Table 5 shows the heat-conductive dielectric polymer material inaccordance with other examples of the present application. The nonwovenfiber component uses glass fiber, polyester fiber or the mixturethereof, and comprises 1%-35%, preferably 2%-30%, and most preferably3%-25% by volume of the heat-conductive dielectric polymer material. Thethermosetting epoxy resin may include bisphenol A epoxy resin andmulti-functional epoxy resin. The multi-functional epoxy resin may beside chain epoxy group epoxy resin or tetra-functional epoxy resin. Thethermoplastic may be phenoxy resin and comprises 1%-40% and preferably2%-30% by volume of the heat-conductive dielectric polymer material. Theheat-conductive filler includes aluminum oxide, and may further includeboron nitride or aluminum nitride. The heat-conductive filler comprises35%-75%, preferably 40%-70% and most preferably 45%-65% by volume of theheat-conductive dielectric polymer material. It can be known from Table5 that all embodiments have high thermal conductivities, which are equalto or greater than 1.5 W/mK, the peeling strengths are equal to orgreater than 0.8 kg/cm (the peeling strengths of the examples except“Example 7” are greater than 1.5 kg/cm), and all examples have superiorvoltage endurance characteristics those are greater than 2000V/0.1 mm,and preferably 3000V/0.1 mm.

TABLE 5 Example 1 2 3 4 5 6 7 Composition bispheonol A 10 18 23 18 18 2522 (vol %) epoxy resin Multi-functional 7 8 13 12 12 10 10 epoxy resinGlass fiber 6 5 5 10 3 10 7 Polyester fiber 4 3 3 0 7 5 0 phenoxy resin23 8 6 2 2 8 7 Aluminum oxide 50 58 50 53 53 0 0 Boron nitride 0 0 0 0 50 54 Aluminum nitride 0 0 0 5 0 42 0 Curing agent Dicy Dicy Dicy DicyDicy Dicy Dicy Physical Thermal 1.5 1.8 1.5 4.5 3.9 3.9 1.8characteristics conductivity (W/mK) Glass transition 105 130 140 150 150130 130 temperature (° C.) Peeling strength 1.85 1.82 1.86 1.61 1.521.81 0.8 (kg/cm) Voltage endurance 52 48 51 50 55 50 48 (KV/mm)

As shown in FIG. 2, the aforementioned heat-conductive dielectricpolymer material can be fabricated to a heat dissipation substrate 20,in which the interfaces between the heat-conductive dielectric polymermaterial layer 23 and the first and second metal layers 21 and 22 mayinclude a micro-rough surface 25 having nodular protrusions 26.According to Table 5, the heat-conductive dielectric polymer materiallayer 23 can withstand a voltage larger than 2000V, and preferably 3000Vin the case that its thickness is 0.1 mm, and the thermal conductivitiesare greater than 1.5 W/mK.

According to the present application, the heat-conductive dielectricpolymer material has IPN structure or nonwoven fiber component, so thatsolid-liquid separation issue will not occur when it is subjected tohot-press. The metal layers may use copper, aluminum, nickel, copperalloy, aluminum alloy, nickel alloy, copper-nickel alloy andaluminum-copper alloy. The heat-conductive dielectric polymer materialis rubbery rather than slurry-like, and thus can be easily stored andprocessed. In the case of addition of thermoplastic, the heat-conductivedielectric polymer material can be made according to commonthermoplastic processing methods, thereby enhancing the processibility.

Table 6 shows coefficient of thermal expansion (CTE) data in X-axis andY-axis of examples in which the heat-conductive dielectric polymermaterial includes nonwoven fibers of different volume percentages. Thepolyester fiber uses polyethylene terephthalate (PET) fiber. Tgindicates the glass transition temperature of the polymer component.Example 1 uses glass fiber “A” only. Example 2 uses both glass fiber “A”and glass fiber “B”. Example 3 and Example 4 further add polyesterfibers. Glass fiber “A” has a length of 12.7 mm and a diameter of 13 μm,and thus its aspect ratio of length to diameter is approximately 970.Glass fiber “B” has a length of 3.2 mm and a diameter of 10 μm, and thusits aspect ratio of length to diameter is approximately 320. Inpractice, the ratio of length to diameter is between 50 and 10000, andpreferably between 150 and 5000, and most preferably between 250 and1000.

TABLE 6 Example 1 2 3 4 Composition Liquid epoxy resin DER331  42.8% 42.8% 43%    41.6% (vol %) Aluminum oxide 50%   50%   50%   50%   Glassfiber A (12.7 mm/13 μm)    7.2%    3.2%    5.7%    5.5% Glass fiber B(3.2 mm/10 μm) 0   4% 0   0   Polyester fiber 0   0      1.3%    2.9%Physical CTE X-axis 22.46 20.05 18.2  13.87 Characteristics (10⁻⁶/° C.,<Tg) Y-axis 29.47 25.86 22.82 16.58 Y-axis/X-axis  1.31  1.29  1.25 1.2CTE X-axis 47.76 41.78 42.14 64.41 (10⁻⁶/° C., >Tg) Y-axis 100.18  66.4365.68 71.25 Y-axis/X-axis 2.1  1.59  1.56  1.11

According to Table 6, Example 1 using glass fiber “A” only has CTE inY-axis of approximately 100×10⁻⁶/° C., and the ratio of CTE in Y-axis toX-axis is approximately 2.1 at a temperature higher than Tg. If amaterial has a CTE and a ratio larger than these values, the heatdissipation substrate containing the material is easily bent. Therefore,it does not meet the requirement for processing. Example 2 uses twoglass fibers of different length-to-diameter ratios to decrease the CTEto below 70×10⁻⁶/° C. and the ratio of CTE in Y-axis to CTE in X-axis isapproximately 1.6 at a temperature higher than Tg. Specifically, theratio of CTE in Y-axis to CTE in X-axis can be lower than 1.6 orpreferably lower than 1.3 by adding polyester fiber with appropriateamount at a temperature higher than Tg. In summary, the ratio of CTE intwo mutually perpendicular axes of the heat-conductive dielectricpolymer material is less than 2.1, preferably 1.6 or most preferably1.3, and the values of CTE in X-axis and CTE in Y-axis are less than100×10⁻⁶/° C., thereby significantly preventing the substrate frombending to increase the processibility. Referring to the examples havingboth glass fiber and polyester fiber of Tables 5 and 6, the volume ratioof the glass fiber to the polyester fiber is between 0.3 and 5, orpreferably between 0.5 and 4.5.

According to the present application, nonwoven fiber component is addedto make the heat-conductive dielectric polymer material rubbery, and theratio of CTE in different axes can be controlled to below an appropriatenumber by modifying the fiber component amount or fiber types, therebysignificantly increasing the processibility.

The above-described embodiments of the present application are intendedto be illustrative only. Numerous alternative embodiments may be devisedby persons skilled in the art without departing from the scope of thefollowing claims.

1. A heat-conductive dielectric polymer material, comprising: a polymercomponent comprising a thermosetting epoxy resin, wherein thethermosetting epoxy resin comprises 4%-60% by volume of theheat-conductive dielectric polymer material; a nonwoven fiber componentuniformly dispersed in the polymer component, wherein the nonwoven fibercomponent comprises 1%-35% by volume of the heat-conductive dielectricpolymer material; a curing agent configured to cure the thermosettingepoxy resin at a curing temperature; and a heat-conductive filleruniformly dispersed in the polymer component, wherein theheat-conductive filler comprises 40%-70% by volume of theheat-conductive dielectric polymer material; wherein the heat-conductivedielectric polymer material has a thermal conductivity greater than 0.5W/mK.
 2. The heat-conductive dielectric polymer material of claim 1,wherein the thermosetting epoxy resin is selected from the groupconsisting of end-epoxy-function group epoxy resin, side chain epoxyfunction group epoxy resin, multi-functional epoxy resin or the mixturethereof.
 3. The heat-conductive dielectric polymer material of claim 1,wherein the nonwoven fiber component is selected from the groupconsisting of ceramic fiber, organic polymer fiber and the mixturethereof.
 4. The heat-conductive dielectric polymer material of claim 1,wherein the nonwoven fiber component is selected from the groupconsisting of glass fiber, aluminum oxide fiber, carbon fiber,polypropylene fiber, polyester fiber and the mixture thereof.
 5. Theheat-conductive dielectric polymer material of claim 1, wherein thenonwoven fiber component is a chopped strand fiber.
 6. Theheat-conductive dielectric polymer material of claim 1, wherein a ratioof CTE in two mutually perpendicular axes of the heat-conductivedielectric polymer material is less than 2.1 at a temperature higherthan a glass transition temperature of the polymer component.
 7. Theheat-conductive dielectric polymer material of claim 1, wherein a ratioof CTE in two mutually perpendicular axes of the heat-conductivedielectric polymer material is less than 1.3 at a temperature higherthan a glass transition temperature of the polymer component.
 8. Theheat-conductive dielectric polymer material of claim 1, wherein CTE ofthe heat-conductive dielectric polymer material is less than 100×10⁻⁶/°C. at a temperature higher than a glass transition temperature of thepolymer component.
 9. The heat-conductive dielectric polymer material ofclaim 1, wherein the nonwoven fiber component comprises glass fiber andpolyester fiber, and a volume ratio of the glass fiber to the polyesterfiber is in the range between 0.3 and
 5. 10. The heat-conductivedielectric polymer material of claim 1, wherein the nonwoven fibercomponent comprises at least two glass fibers of different ratios oflength to diameter.
 11. The heat-conductive dielectric polymer materialof claim 1, wherein the nonwoven fiber component comprises a glass fiberof a ratio of length to diameter ranging from 50 to
 10000. 12. Theheat-conductive dielectric polymer material of claim 1, wherein thethermosetting epoxy resin is uncured liquid epoxy resin or polymerizedepoxy resin.
 13. The heat-conductive dielectric polymer material ofclaim 1, wherein the thermosetting epoxy resin comprises mono-functionalgroup, bi-functional group, tri-functional group, multi-functional groupor the mixture thereof.
 14. The heat-conductive dielectric polymermaterial of claim 1, wherein the thermosetting epoxy resin comprisesphenolic epoxy resin or bisphenol A epoxy resin.
 15. The heat-conductivedielectric polymer material of claim 1, wherein the curing agent has acuring temperature higher than 80° C.
 16. The heat-conductive dielectricpolymer material of claim 1, wherein the polymer component furthercomprises a thermoplastic, and the thermoplastic and the thermosettingepoxy resin are mutually soluble prior to curing and form aninter-penetrating network structure after curing.
 17. Theheat-conductive dielectric polymer material of claim 16, wherein thethermoplastic comprises 1% to 40% by volume of the heat-conductivedielectric polymer material.
 18. The heat-conductive dielectric polymermaterial of claim 16, wherein the thermoplastic comprises bisphenol Aepoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin or themixture thereof.
 19. A heat dissipation substrate, comprising: a firstmetal layer; a second metal layer; and a heat-conductive dielectricpolymer material layer comprising the heat-conductive dielectric polymermaterial of claim 1, wherein the heat-conductive dielectric polymermaterial layer is sandwiched between and in physical contact with thefirst metal layer and the second metal layer; wherein theheat-conductive dielectric polymer material layer can withstand avoltage greater than 2000V in the case that the heat-conductivedielectric polymer material layer has a thickness of 0.1 mm.
 20. Theheat dissipation substrate of claim 19, wherein interfaces between theheat-conductive dielectric polymer material layer and the first andsecond metal layers comprise at least one micro-rough surface having aplurality of nodular protrusions.
 21. The heat dissipation substrate ofclaim 19, wherein peeling strength between the heat-conductivedielectric polymer material layer and the first or the second metallayer is greater than 0.8 kg/cm.